At present, a rear cover made of metal has become a popular structure for a number of brands of cellphones, and an N-type metal rear cover is a recently prevalent three-section structure. Generally, a cellphone having the N-type three-section metal rear cover can form a GPS/WIFI antenna system by coupling its frame with different antenna units. Basically, a mainboard of the antenna system is merely provided with a grounding point and a feeding point for connecting with external components, so that during a debugging process of the antenna system, the mainboard can be conveniently connected with the antenna system. However, since internal components of different cellphones may have different arrangements, or profiles of the N-type three-section metal frames of different cellphones may also be different, a required structural design of the antenna and radio frequency network design of the system mainboard will be different accordingly. Therefore, during debugging, it is necessary to try a variety of implementation manners of the antenna structure. Moreover, in some implementing manners, only one frequency network source is required, some may require two frequency network sources, some may require a plurality of grounding points, and some may require to use a tuning switch. As a result, it is needed to create various mainboards to achieve antenna debugging through different combinations, which will inevitably increase manufacture cost.